Amorphous, open-ended, unstructured time, with undercurrents of foreboding, pockets of boredom and fleeting interludes of peace or reassessment. That’s what Covid-19 has brought to many people — and it’s a mental state that Brian Eno’s vast recorded catalog has been prepared for since he first popularized the term “ambient music” in the 1970s. The long days and featureless nights of self-quarantine offer an opportune moment to revisit — or get acquainted with — Eno’s time-warping music.

He does have other skills. On four solo albums from the 1970s, after he left Roxy Music, Eno thoroughly mastered rock-song structure, with slyly cerebral lyrics and skewed instrumental sounds; all four albums are gems, particularly “Before and After Science” from 1977. He has intermittently made song albums in the decades since. And his 1981 collaboration with David Byrne on “My Life in the Bush of Ghosts” — shaping found-sound sampled vocals from international sources into rhythm-driven, club-ready tracks — opened new doors in dance music.

But for the most part, Eno has channeled his pop impulses into production and collaborations — with U2, David Bowie, Talking Heads, John Cale and lately Karl Hyde of Underworld. Yet the bulk of his own recordings, and all of those selected here, are instrumentals that, old or new, are particularly suited to orchestrate this uneasy historical moment.

Eno was not the first to make music designed to maintain a subliminal, atmospheric presence while evading the foreground. By his account, medical circumstance led him to thinking about music as just one element in a larger environment. When he was immobilized after an automobile accident, a friend left music playing on a record player he couldn’t reach, at such low volume that it melded with all the other sounds in the room; Eno being Eno, he ended up listening with John Cage-like attentiveness. That gave him the idea for his quiet, ambient (although he hadn’t yet settled on the term) 1975 album, “Discreet Music.” Soon, Eno would stake out an ambient music genre that has since been populated by countless composers alongside him.

Yet Eno himself has continued to rework what ambient music might mean with continual flexibility, shifting his approaches and adapting constantly to new technology and circumstances. He has released multiple albums per year throughout a four-decade solo career — including, this year, “Mixing Colours,” a collaboration with his brother Roger Eno. There are clearly sounds he is drawn to repeatedly: glimmering reverberant timbres, uncannily sustained chords and clusters, melodic phrases that shy away from turning into melodies. But his catalog holds ample exceptions to any generalization about his music.

Eno has improvised in the studio, alone or with collaborators, using real time recordings or making surreal edits. He has composed extremely short ambient works — like the six-second Windows 95 start-up sound — and potentially endless ones. He has made music that seems cyclical and music that hints at narrative. For decades, he has created generative music: systems that are set in motion, like loops of irregular length or permutations of computer-generated tones, and chosen particular results like a favorite bolt of a textile. He edits, manipulates and recombines his recordings, or he allows his generative music to flow freely, as he has done with installations in galleries, museums, hospitals and public spaces. He has worked by concept, by instinct, by collaboration and by every conceivable combination of them all.

‘The Heavenly Music Corporation 1’ (Fripp & Eno, 1973)

Eno and Robert Fripp (King Crimson’s guitarist) experimented in the early 1970s with looping — which, back in the analog era, involved routing a tape through two tape recorders, to layer the recording from the first one with the playback from the second. The loop sets up a pulsating drone in “The Heavenly Music Corporation 1,” topped by lead-guitar solos from Fripp that claw and flail, then braid themselves back into the drone: aggression patiently reframed. (Note: Although streaming services break the piece up into tracks, it’s worth hearing as an uninterrupted whole.)

‘Discreet Music’ (1975)

The title track of Eno’s first solo ambient breakthrough loops and undulates for just over half an hour, with endlessly recurring, somehow optimistic two-note and four-note motifs that float in an amniotic bath of consonances. The reedy electronic tones suggest woodwinds played by musicians who never have to pause for breath.

‘1/1’ (1978)

Eno officially claimed the term “ambient” with “Ambient 1/Music for Airports,” an LP of four tracks that showed diagrams of how their loops intersected on the album cover. Its opening track, functionally titled “1/1” and credited to Eno, Robert Wyatt (who played the piano) and Rhett Davies, could have been complete in its first 20 seconds: a piano phrase answered by its tonic chord, all neatly resolved. But after a pause, the phrase recurs and extends, joined by other motifs and consoling notes in other timbres, each pausing and resuming at its own leisurely pace. The phrase isn’t leading anywhere; it’s circling, waiting, not giving away how long its particular limbo might last.

‘The Chill Air’ (Harold Budd and Brian Eno, 1980)

For “Ambient 2: The Plateaux of Mirror,” Harold Budd improvised on pianos that Eno had treated with electronics: altering their tone, bringing out certain resonances, triggering synthesizers. In “The Chill Air,” the treatments are faint afterimages and anticipations, subtly revealing themselves as Budd plays measured counterpoint, mostly just two notes at a time, tiptoeing with a purpose.

‘The Lost Day’ (1982)

On his 1982 album, “Ambient 4: On Land,” Eno evoked landscapes by incorporating natural sounds, placing the music outside the studio. “The Lost Day” hints at gusty winds and the clanging of distant bell buoys, guidance through a treacherous harbor; dramatic cello-like lines arise and drift away, as if swallowed up by a haze.

Much of “Apollo: Atmospheres and Soundtracks” is as sparse as an airless lunar vista. “An Ending (Ascent)” is lush by comparison: slow, breathy-toned, slightly blurred major-key chords that suggest a miniaturized processional, a ritual happening in reduced gravity.

‘Lanzarote’ (1992)

Inescapable foreboding and disquiet run all the way through “The Shutov Assembly,” from 1992, which may well be Eno’s bleakest, most dissonant album. “Lanzarote” draws suspense from what might seem, in prospect, to radiate stability. For much of its length, a single note arrives in assorted keyboard tones in different octaves, low and high, from tolling bass to solitary piano to distant cricket-like overtones to hints of organ and orchestra. But other sustained notes waft in to dispute and displace that tonal center, so there’s no secure resting place.

‘Neroli’ (1995)

The 57-minute “Neroli” is an exercise in austerity: a fixed bass note tolling irregularly behind a lugubrious keyboard line that stops and starts, wandering fitfully within a small, circumscribed range and in a vaguely Asian-sounding mode. Deep in the background, other sustained tones loom. Eno subtitled it “Music for Thinking IV,” suggesting that it wouldn’t be distracting; it’s monolithically reticent.

‘Transmitter and Trumpet’ (Brian Eno and Jah Wobble, 1995)

Eno wrote music for a film about the filmmaker Derek Jarman and decided the tracks weren’t strong enough on their own for a soundtrack album. So he sent them to Jah Wobble, the bassist from Public Image Ltd., who reworked them by himself in a hands-off collaboration. “Transmitter and Trumpet” sprouts a brisk six-beat bass line that appears and disappears and beams in a world of influences: orchestras, electronics, Morocco, India, West Africa. And then it obscures them in echoes, static and numerous layers of warped sounds — disorienting but always in motion.

‘Calcium Needles’ (Brian Eno, Jon Hopkins and Leo Abrahams, 2010)

Eno made “Small Craft on a Milk Sea” with Jon Hopkins, a dance-music D.J.-producer, and Leo Abrahams, who plays guitar and other instruments; the album mixed song-length, melodic tracks with far more abstract ones like “Calcium Needles.” The track courts vertigo, following descending bell tones into a bottomless, reverberating abyss.

‘Marsh Chorus’ (Tom Rogerson with Brian Eno, 2017)

The album “Finding Shore” is a collaboration with the keyboardist Tom Rogerson, from the band Three Trapped Tigers. Rogerson improvised on piano; Eno manipulated the sounds as Rogerson played and responded. The piano sounds more or less natural through much of the album, but on “Marsh Chorus,” Eno transforms its tone into a hybrid of harpsichord and carillon and turns some notes into insistently pinging loops. Rogerson plays decisive, declamatory phrases and lets things shimmer in between. There are bird sounds, too.

‘Reflection’ (2017)

Near-stillness prevails through most of the hourlong “Reflection,” along with stereo-ricocheting tones that live up to the piece’s title. It’s a generative piece, with one form including an iOS app, so the streaming and CD versions of “Reflections” are only a few of its countless shapes. Its materials are bell tones, endlessly sustained string-like and clarinet-like notes, a shivery undercurrent and elusive, flitting pockets of echo. Although it is generated via software with some of Eno’s familiar ingredients, “Reflections” is far from homogeneous. It’s more like a suite, with sections of relative activity and virtual stasis; almost up to the end, new sounds emerge. (For the impatient, Eno also released a four-minute excerpt.)

‘Surbahar Sleeping Music’ (2018)

Eno’s six-CD collection of “Music for Installations” gathered music he has written for site-specific works since the 1980s; it includes “Surbahar Sleeping Music” among its “music for future installations.” A surbahar is larger, lower-pitched relative of the sitar, and this 18-minute drone piece, with no fixed beat or pulse, sounds like it’s constructed from notes plucked on the surbahar, on their own and electronically manipulated, richly radiating upward from deep, plangent bass tones.

‘Only Once Away My Son’ (Eno with Kevin Shields, 2018)

It was probably inevitable that Eno would eventually collaborate with Kevin Shields of My Bloody Valentine, a fellow wielder of edgeless, untraceable, overwhelming sounds. “Only Once Away My Son” is the instrumental half of a 2018 single — its lyrics appear in the other track, “The Weight of History” — and it’s a speaker-challenging tempest of drone and distortion, lingering to reveal sustained turbulence at every level, overloading even more and then somehow solidifying into a single note.

‘Burnt Umber’ (Brian Eno and Roger Eno, 2020)

Eno’s latest collaboration with a keyboardist is “Mixing Colours,” an album made with his younger brother, Roger, whose own music tends to be prettier and more straightforwardly melodic than Brian Eno’s work. “Burnt Umber” is a melancholy waltz, a melody unfolding in slightly cracked bell tones over a somber four-note bass vamp, calmly disconsolate.